[ardour-dev] **Caution-External**: Re: Live Mixdown

[Urbansound]

----- Original Message ----- 
From: "Thomas Vecchione" <seablaede at gmail.com>
To: "Urbansound" <urbansound at sbcglobal.net>
Sent: Wednesday, January 11, 2006 11:28 PM
Subject: Re: [ardour-dev] **Caution-External**: Re: Live Mixdown


>> 8-O I'm wondering then, why the Gain controls would not function in that 
>> instance?  VNC is simply remoting the mouse/key states between two 
>> machines, yes?

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>> but would VNC really affect any of this, or is that
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>> simply the case where a digital snake is carrying audio data only?


> There is a difference between Volume sliders in Ardour and gain controls 
> on a pre or other audio device.  They can have similar end results, but a 
> proper gain structure is important for a decent sound, and having the 
> gains set correctly at the pres is important.

Thx Seablade,

Certainly the two are distinctly different as to the extent of gain beyond 
unity, versus voltage displacement of the given gain level.  The question 
was .... if the Ardour unit is at the stage and controlled via remote VNC at 
FOH, then why would I not be able to adjust the gain at the master unit on 
the stage, by tweaking the widget for gain, on the VNC client machine, FOH?

True that gain config will be dependant on card, method, layout, etc., but 
given a card with gain available and that I have the ability to access the 
card's gain function in a device mode that presents it as available, then 
why would I lose the ability to tweak the pseudo-analog little knob on the 
FOH VNC machine and have the gain adjust on the remote station?

How could VNC possibly affect this solution with all of the horsepower, 
cards, fanning, inputs and outputs right there at the stage?


>> Indeed, some of the benefits I'm hoping  for with Ardour, are the live 
>> compressor/delay/reverb potential of such a system and localizing it on 
>> stage, given the VNC concept, especially.

> Just out of curiosity how many channels/pieces are you running?

Test driving two junk, stereo sound cards to learn setup soon.
Installation will accommodate 8 LCR/1/4 Hi/Lo-Z inputs, 2 monitor outs and 2 
main outs.

>And why go this route instead of the traditional analog route with some 
>decent equipment that may very well get you better results.  If you are 
>just doing it for the effects/processing and the like I would say insert 
>the computer into the channels of an analog board and do it like that.

Expansion is to 32 channels ~ 6-8 months.
Integrated Video potential for central control.
Overall cost per input, given flexibility in full.
Advancing "with" technology is best, imho (save for latency).

>> Don't like the long MIDI run approach where levels can invite drops or 
>> demand repeaters adding the potential of component failure or data 
>> corruption.

> Well personally a control surface would be a must with me.

Can you offer a link or description and I'll have a look.  I understand the 
desire but given that Ardour is open source and I can interface automation 
to the devices direct therefore, plus a secure booth area during 
performance, I'm fairly secure mousing will be minimal as we will run 
"Programmed segments" that an operator just keeps queuing and launching. 
Again, a select and change, simple device would be good, but examples always 
speak volumes, if you have any?  ;-)

> But out of this setup Midi failure would be the least of my worries.  Had 
> a conversation recently about this on the Theater Sound mailing list I am 
> part of and it was pretty well decided that while the standard only reads, 
> what is it 25 feet or something tiny like that, it is well more than 
> capable with STP wiring to run several hundred feet.  UTP shouldnt be much 
> of a problem either.  Personally I am looking at running it 300 feet 
> myself on my next show.

The simple explanation is imho ... Today that's feasible to do, converting 
the data to fiber, if you have a clever fella to do it.  It's not a 
difficult design at all as MIDI data is essentially a serial communication 
with On/Off states surrounding 5 vdc.  Oddly, if you could attach a fiber, 
directly to each midi device fiberoptic isolator, you  wouldn't even need a 
converter.  LOL !!

The sticky explanation is this...

The spec is as follows...

----- Design is set with a jumper for either positive or negative going 
pulses

----- when jumper is pulling inputs to +5 VDC the input is pulled up by 22k 
ohms
----- < 1VDC for at least 24 ms (switch closed) then a note is sent
----- > 4VDC switch open and no note is sent
----- between 1 VDC & 4 VDC is undefined

----- when jumper is pulling inputs to GND the input is pulled down by 22K 
ohms
----- < 1 VDC switch open and no note is sent
----- > 4 VDC for at least 24 ms (switch closed) then a note is sent
----- between 1v & 4v is undefined

Why not STP?..., (Strand Twisted Pair)

What wire guage will you use to handle what voltage/amperage over 300 feet? 
As an opto-isolator driven interface, the biggest resistor in the path of 
conduction is a 220 ohm resistor, normally, which you are going to put in 
series with the resistance of your STP over 300 feet.  Resistance in series 
combine and drop their loads accordingly, i.e. the conductor is a resistor, 
= voltage drop.

STP's only benefit is "some" cancellation of induced AC noise, given the 
twisted pair and given the resulting impedance, distance and environment, 
coaxial is needed.  ARRRG  Did the conversation include voltage drop and 
wire guage reliability/conductivity? Because no STP manufacture will give a 
guarantee and STP is not a quality conscious product.  The problem will be 
1)_ Voltage drop, resulting in increased current.  2_Increased heat will be 
expended on the input side of the instrument optical-isolator which will let 
the smoke out, usually sooner than later.   Here are the MIDI hardware 
designs... http://www.midi.org/images/midiadap.gif  and 
http://www.midi.org/about-midi/electrical.shtml

Lets talk about pulse width elongation and the effects it has on clock/data 
sync / stability.  The master timing clock is sent 24 times per quarter 
note, but requiring a 24 millisecond on or off state to be reliable, which 
of course is sensitive to the signature tempo and can itself chug along at 
512 bpm, if I recall.  In considering what things can be done with midi, you 
may see change data sequences at 1/512th note, running at 512 bpm.  Now, tax 
that with variations in voicing and other change data, and you'll find that 
even if you could beef up your MIDI toys to handle it or use big wire 
practically, the lengthening of clock pulse and increments will result in 
collisions if delay occurs.  i.e the on and off conditions will extend in 
duration proportionally to the amount of elongation and may whack each other 
or have a very odd result with regard to whether or not the serial data 
begins to float into the non-data voltage domain.

So, just because someone "Says" you can do it, consider the premature loss 
to equipment and the mundane nature of big conductors for long distance, or 
at least test on a disposable instrument and run it 3 weeks, 24/7 if it 
will.  The specification is 50 feet for a reason and cost control for 
manufacturing dictates that limit, for warranty and best longevity.  See 
what you're friends at the Theater Sound mailing list find in this 
explanation and maybe drop me a direct reply.  I'd be interested in their 
take.

Hope it helped some.

Mike

>       Seablade